From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757285Ab1DKJMD (ORCPT ); Mon, 11 Apr 2011 05:12:03 -0400 Received: from mx3-phx2.redhat.com ([209.132.183.24]:49700 "EHLO mx3-phx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752326Ab1DKJMB convert rfc822-to-8bit (ORCPT ); Mon, 11 Apr 2011 05:12:01 -0400 Date: Mon, 11 Apr 2011 05:11:28 -0400 (EDT) From: Takuma Umeya To: Stefan Hajnoczi Cc: virtualization@lists.linux-foundation.org, Stephen Hemminger , linux-kernel@vger.kernel.org Message-ID: <1526578879.12280.1302513088278.JavaMail.root@zmail07.collab.prod.int.phx2.redhat.com> In-Reply-To: Subject: Re: [PATCH] virtio: decrement dev_index when device is unregistered MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-Originating-IP: [10.5.5.72] X-Mailer: Zimbra 6.0.9_GA_2686 (ZimbraWebClient - FF3.0 (Linux)/6.0.9_GA_2686) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- Original Message ----- > On Tue, Apr 5, 2011 at 5:49 AM, Takuma Umeya > wrote: > > When virtio device is removed, dev_index does not get decremented. > > The next device hotplug event results in consuming the next pci to > > the one that is suppose to be available. > > > > Signed-off-by: Takuma Umeya > > > > diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c > > index efb35aa..67fe71d 100644 > > --- a/drivers/virtio/virtio.c > > +++ b/drivers/virtio/virtio.c > > @@ -216,6 +216,7 @@ EXPORT_SYMBOL_GPL(register_virtio_device); > >  void unregister_virtio_device(struct virtio_device *dev) > >  { > >        device_unregister(&dev->dev); > > + dev_index--; > > I don't think there is any guarantee that virtio devices are > added/removed in first-in-last-out order. > > That means I could add a virtio-net device (index 0) followed by a > virtio-blk device (index 1). Now I remove the virtio-net device > (index 0) which causes me to decrement dev_index and hand index 1 out > again to the next device. This leaves us with virtio-blk (index 1) > and the new device with index 1, which is not unique. > > Perhaps I missed a constraint which prevents this from occurring? I believe the address is assigned up to 1f so using u32 value to track use/free. This should make the code immune to the scenario. Would this be adequate? diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c index efb35aa..0c73507 100644 --- a/drivers/virtio/virtio.c +++ b/drivers/virtio/virtio.c @@ -3,7 +3,7 @@ #include /* Unique numbering for virtio devices. */ -static unsigned int dev_index; +static u32 dev_index; static ssize_t device_show(struct device *_d, struct device_attribute *attr, char *buf) @@ -187,12 +187,23 @@ EXPORT_SYMBOL_GPL(unregister_virtio_driver); int register_virtio_device(struct virtio_device *dev) { - int err; + int err, count; + u32 testbit; + + count = 0; dev->dev.bus = &virtio_bus; /* Assign a unique device index and hence name. */ - dev->index = dev_index++; + while (count < 32){ + testbit = 1UL << count; + if(!(dev_index & testbit)){ + dev->index = count; + dev_index |= testbit; + break; + } + count++; + } dev_set_name(&dev->dev, "virtio%u", dev->index); /* We always start by resetting the device, in case a previous @@ -215,7 +226,13 @@ EXPORT_SYMBOL_GPL(register_virtio_device); void unregister_virtio_device(struct virtio_device *dev) { + u32 removebit; + + removebit = 1UL << (dev->index); + device_unregister(&dev->dev); + + dev_index ^= removebit; } EXPORT_SYMBOL_GPL(unregister_virtio_device); > > Stefan